In, for example, GSM systems, the so called A interface is used to connect nodes in a Radio Access Network to nodes in a Circuit Switched Core Network. The nodes in the Radio Access Network can, for example, be a Base Station Subsystem, a BSS, which in turn comprises a Base Station Controller, a BSC, and one or more Base Transceiver Stations, BTS. An example of a node in the Circuit Switched Network to which the BSC or the BTS connect over the A interface is a Media Gateway, an MGw.
Recently, support has been introduced in GSM for user plane traffic over the A interface by means of the Internet Protocol, IP, so called AoIP, using an RTP connection for user plane data and an associated RTCP connection for control signaling.
In the RTP connection, the nodes at both ends of the connection will have an RTP address for the RTP connection, with the RTP address comprising an IP address and a UDP port. The associated RTCP connection will have the same IP address but a different UDP port.
In a GSM AoIP connection in which a node in a BSS is connected to a node such as, for example, a Media Gateway, MGw, in a Circuit Switched Core Network, either the BSS or the MGw can have a need to change its RTP address, i.e. either the IP address or the UDP port of the RTP address, or both of those parameters.
In order to handle such changes, a handover procedure has been introduced in the GSM standard. This standardized handover procedure is referred to as “Internal BSS Handover with MSC support”, and is defined in 3GPP TS 48.008 Rel-8 and onwards. The MSC is a Mobile Switching Centre associated with the MGw in question.
The Internal BSS Handover with MSC support is useful, but causes an increased load on the A interface as well as on the nodes at both ends of the A interface.